To provide a lens unit or the like having high imaging quality by fixing a lens by a method for reducing influence on an optical functional surface of the lens and other parts when housing the lens in a barrel.

The lens unit 2 includes: a first lens 4 having an optical functional surface 4a to condense and emit incident light, and a flange part 4b formed on the outer circumference of the optical functional surface 4a; a second lens 6 having an optical functional surface 6a to condense light emitted from the first lens 4 and a flange part 6b formed on the outer circumference of the optical functional surface 6a; and the barrel 2a having a housing part 2e to house the first lens 4 therein, and house the second lens 6 so that the flange part 6b of the second lens 6 may be superposed on the flange part 4b of the housed first lens 4, wherein the second lens 6 is fixed in the housing part 2e by subjecting the flange part 6b of the second lens 6 to laser-welding.